Various resorbable (occasionally referred to as absorbable or "remodelable") materials presently exist for use in prosthetic applications, e.g., as patches, implants and/or as components of prosthetic devices.
Synthetic resorbable materials made from the polyesters, polylactide and polyglycolide, for example, have found use in various fields of medicine (See, e.g., Ashammaki, N. A., J. Biomed. Mater. Res., 33: 297-303; 1996). Versions of these materials exist commercially under the tradenames Vicryl.RTM. (Ethicon, Inc.) and Dexon.RTM. (Davis & Geck, Inc.). The gradual decomposition of these polymers is facilitated by hydrolysis, and catalyzed by biochemical action of the host tissues (Hanbrough, J. F., et al., J. Burn Care Rehab., 14: 485-494; 1993). These materials may be produced as membranes or as woven mesh in the case of producing resorbable suture.
While synthetic resorbable materials are a rather recent phenomenon, collagenous materials have been used as prosthetic grafing for many years; as in the case of lyophilized human dura, dating back to 1954. As a common practice for several years, such collagenous materials have been crosslinked with an agent such as glutaraldehyde, in order to diminish the antigenicity of a xenograft while increasing its resistance to enzymatic degradation produced by host tissue responses (Gratzer, P. F., et al., J. Biomed. Mater. Res., 31: 533-543; 1996). Polyepoxy compounds have also been used for such purposes, however are more stable with regard to the resulting alkylated amines in the collagen (Sung, H-W., et al., J. Biomater. Sci. Polymer Edn., 8: 587-600; 1997). While crosslinked tissues work well as long-term implants, they are not resorbable and as such, do not promote host tissue remodeling, or in turn, the eventual replacement of a graft by the body itself.
Aesculap AG & Co. (B. Braun Surgical) offers products under the tradename Lyoplant.RTM., in the form of a bovine pericardium-based resorbable replacement for dura mater. Lyoplant.RTM. is produced by a process that involves mechanical removal of adherent fat and connective tissue, chemical treatment to inactivate enzymes and potential pathogens, freeze-drying, cutting to various sizes, packaging and terminal sterilization with ethylene oxide. The product is indicated to be used for covering cerebral and cerebellar dural defects, for decompressive duraplasty in cases of increased intracranial pressure, for covering spinal dural defects and for spinal decompressive duraplasty. This material has been observed to be fully remodeled within one year after implant.
Tutogen Medical, Inc. provides processed pericardium products under the tradename Tutoplast.RTM., in the form of a solvent-dehydrated, gamma-irradiated preserved human pericardium. The processing of Tutoplast.RTM. tissue involves thorough cleaning, processing, dehydration and preservation. The process is said to leave no deleterious residue and minimizes antigenic potential. Collagenous connective tissue with multidirectional fibers retains the mechanical strength and elasticity of native pericardium, while providing the basic formative structure to support replacement by new endogenous tissue. This tissue is indicated for use in a variety of surgical applications, including duraplasty (as a substitute for human dura mater), and in abdominal, urological, opthalmological, and vascular surgery. The absorption process and reformation of endogenous tissue begins one to two days after implantation and continues for weeks, months, or years, depending on the size of the graft and the responsiveness of the graft site. Mentor Corporation has entered a strategic alliance with Tutogen Medical, Inc., to use the Tutoplast.RTM. technology to manufacture resorbable slings for urinary incontinence (Suspend.TM.).
A variety of other uses of resorbable materials are described in the patent literature. See, for instance, U.S. Pat. No. 5,895,420 (Mirsch, II, et al., "Bioresorbable Heart Valve Support"), which, relates to bioprosthetic heart valve stents that are fashioned of resorbable materials. Such stents may be configured as sheaths or frames contoured to the shape of a valvular graft. The stents are eventually resorbed by the patient, leaving a functional "stentless" valve with improved hemodynamic characteristics compared to stented valve implants.
Various other resorbable materials have been suggested or proposed for use with vascular of non-vascular implants. For example, Goldberg et al., U.S. Pat. No. 5,085,629 discloses a biodegradable infusion stent for use in treating ureteral obstructions. Stack, et al., U.S. Pat. No. 5,306,286 discloses an absorbable stent for placement within a blood vessel during coronary angioplasty. Duran, U.S. Pat. No. 5,376,112 discloses an annuloplasty ring to be implanted into the heart to function together with the native heart valve.
In another aspect, U.S. Pat. No. 5,837,278 (Geistlich, et al., "Resorbable Collagen Membrane for Use in Guided Tissue Regeneration"), describes the use of a collagen-containing membrane in guided tissue regeneration. The patent provides a resorbable collagen membrane for use in guided tissue regeneration wherein one face of the membrane is fibrous thereby allowing cell growth thereon and the opposite face of the membrane is smooth, thereby inhibiting cell adhesion thereon.
Finally, see U.S. Pat. No. 5,413,798 (Scholl, et al.) which describes a process for treating bovine pericardial tissue to increase resistance to biological degradation by wet-chemical processing. The use of the tissue is exemplified in the form of an implant which, after three and six months post implantation, was well integrated so that it was no longer distinguishable from autochthonous dura (revitalized by fibrocytes and traversed by blood vessels in the marginal zones). The inner side of the implant is coated with the same cell type as the autologous dura.
On yet another topic, certain articles describe basic research directed to studying the effect of alkylating agents on materials such as collagen. See, for example, Sung, H. W., et al., J. Biomed. Mater. Res. 37:376-383 (1997) and Tu, R. et al., J. Biomed. Mater. Res., 28:677-684 (1994). To the best of Applicants' knowledge, however, no such reference suggests the manner in which such materials might be used in vivo, nor in turn, do they address the question of whether sucb materials can be tolerated, let alone resorbed and remodeled, by the body.
The present assignee is recognized as a leader in the development and manufacture of pericardium based materials. See, for instance, U.S. Pat. Nos. 5,752,965; 5,575,803; 5,549,628; 5,503,638; and 4,915,113 and International Application No. US98/25674, the disclosures of each of which are incorporated herein by reference. Generally, the pericardium materials are crosslinked, e.g., using glutaraldehyde, and hence are typically considered non-resorbable. Such materials have been used in a variety of applications, including as patches, suture and staple line buttress members, and pledgets.